XML

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Date added 22 August 2007
Last edited 12 November 2009

Full Title

Extensible Markup Language (XML)

Description

Extensible Markup Language (XML) is an open standard recommended by W3C as general purpose markup language. It is a profile of ISO 8879 - Standard Generalized Markup Language (SGML), which was defined to enable data to be shared across multifarious information systems, primarily the Internet.

The design of XML achieved the 10 goals stated in the specification:

XML shall be straightforwardly usable over the Internet.

XML shall support a wide variety of applications.

XML shall be compatible with SGML.

It shall be easy to write programs which process XML documents.

The number of optional features in XML is to be kept to the absolute minimum, ideally zero.

XML documents should be human-legible and reasonably clear.

The XML design should be prepared quickly.

The design of XML shall be formal and concise.

XML documents shall be easy to create.

Terseness in XML markup is of minimal importance.

XML implementations rely on data being validated against a Document Type Definition (DTD) or Schema, which formally define data syntax. These are generally developed, and standardised, within communities of interest and thousands of examples exist eg MathML, GML, EAD, METS, SVG.

A wide range of standards which support XML have been published. Exstensible Stylesheet Language (XSL) allows XML to be transformed into a different version of XML, Hyper Text Markup Language (HTML) or another suitable format. A number of extensions allow more complex manipulations of XML data. These include:

XPath - allows reference to individual parts of an XML document

XQuery - allows and XML document to be queried and return a value

XInclude - allows XML documents or parts of XML documents to be merged

XML Encryption - allows XML documents to be encrypted

XML Version 1.1 (second edition) extends XML Version 1 to allow scripts and characters included after version 2.0 of Unicode to be used for attribute and element names. It also allows any Unicode character, whatever the version to be used in data and attribute values. Version 1.1 is not widely used and implementations are only recommended by those who need to use the unique features.

Further Information

Alternative Current Version

XML Version 1.1 (second edition) extends XML Version 1 to allow scripts and characters included after version 2.0 of Unicode to be used for attribute and element names. It also allows any Unicode character, whatever the version to be used in data and attribute values. Version 1.1 is not widely used and implementations are only recommended by those who need to use the unique features. Corrected by <a href=http://www.w3.org/XML/xml-V11-2e-errata> XML 1.1 Second Edition Specification Errata </a>